1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting device and a method for manufacturing the same.
2. Description of the Related Art
Conventional nitride semiconductors include, for example, a GaN nitride semiconductor. Such a GaN nitride semiconductor is used for an optical device of blue/green LEDs, and high-speed and high-power devices, such as MESFET and HEMT. In particular, the blue/green LEDs can be manufactured in mass-production and have been increasingly used in the world.
Especially, in the fields of the GaN nitride semiconductors, a semiconductor light-emitting device having a crystal layer where a group-II element, such as magnesium (Mg) or zinc (Zn), is doped in a region including Ga is spotlighted as a blue light-emitting device.
As shown in FIG. 1, such a GaN nitride semiconductor includes a light emitting device having a multi quantum well structure. This light emitting device is generally grown on a substrate 1 including sapphire or SiC. In addition, a multi-crystalline layer, such as an AlyGa1-yN layer, is grown from the sapphire substrate or the SiC substrate 1 as a buffer layer 2 in the low growth temperature and a GaN under layer 3 is sequentially deposited on the buffer layer 2 in the high temperature condition. An active layer 4 is aligned on the GaN under layer 3 for the purpose of light emission, and an AlGaN electronic barrier layer 5 doped with magnesium Mg and converted into a p-type through an annealing process, an InGaN layer 6 doped with magnesium, and a GaN layer 7 doped with magnesium are sequentially deposited on the active layer 4.
In addition, insulating layers are formed on the GaN layer 7 doped with magnesium and the GaN under layer 3. In addition, a P-electrode 9 and an N-electrode 10 are formed on the GaN layer 7 doped with magnesium and the GaN under layer 3, respectively, thereby forming the light emitting device.
The buffer layer adopted to realize the nitride light emitting device or an optical device, such as a laser device, may attenuate stress between the substrate and a layer grown on the substrate, so the buffer layer including GaN or AlGaN is grown on the substrate including SiC or Si.
However, since the lattice constant of the buffer layer is greatly different from that of the substrate, lattice defects, such as dislocation or vacancy, may occur between the buffer layer and the substrate or between the buffer layer and a layer formed on the buffer layer.
Although such dislocation, defects and an electronic field formed in crystal are disadvantageous to the light emitting device, the nitride semiconductor material is spotlighted as a material for the high-power light emitting device due to quantum dots formed in the InGaN and GaN epitaxial layer used as an active layer. Such quantum dots may laterally confine or localize the carrier (electrons and holes), thereby significantly reducing a bad influence derived from the dislocation or electronic field.
In detail, in the active layer having the quantum well structure, electrons in the conduction band and holes in the valence band are defined within the quantum dot, so that the density of state of the electrons and holes existing in the quantum dot may increase, thereby effectively increasing recombination efficiency between electrons and holes.
In order to form such a quantum dot, the active layer of the conventional nitride semiconductor light emitting device includes indium (In). At this time, the content of indium (In) is about 14% to about 18%. In order to increase the content of indium (In), a method of lowering the growth temperature for the active layer or a method of increasing an amount of indium (In) has been suggested. However, if the growth temperature for the active layer is lowered, the crystalline quality of the active layer is significantly degraded, exerting bad influence upon the reliability of the light emitting device. In addition, if the amount of indium (In) is increased, segregation of indium (In) and phase separation may occur. Especially, in the case of the multi quantum well structure, defect may occur at the interfacial layer formed between active layers, so that the reliability of the active layer is significantly degraded.
Thus, it is very important for improving light emitting efficiency of the nitride semiconductor light emitting device to develop technologies capable of controlling the quantum dot of the active layer.